To obtain a weight measurement in the field on vehicles such as commercial trucks and airplanes requires the use of a portable scale. These portable scales utilize relatively low profile load cells therein that are normally comprised of a piston that interacts with a diaphragm that is part of a hydraulic chamber. In the static condition, the weight disposed on the piston is evenly dispersed over the diaphragm and the piston is stationary. However, when moving the vehicle onto the scale, there are a number of undesirable forces that can be transmitted to the load cells in the scale. These result from forces directed to the surface of the load cell that are off normal, that is, at an angle with respect to the perpendicular. These forces can cause the piston to exert a strong lateral force against the diaphragm which can cause damage to the load cell. In addition, the piston can be moved off center with respect to the hydraulic chamber, thus resulting in inaccurate measurements in that most load cells are designed and calibrated with the piston in the center thereof.
One approach to solving the problem of centering the piston in a load cell is disclosed in U.S. Pat. No. 3,633,695 issued to C. D. Bradley. The Bradley device utilizes a bridge ring on the upper and lower peripheries of a floating piston. The bridge rings are fabricated from hardened steel with a series of slots formed about the periphery thereof. The bridge ring imparts a compressive force to the piston to maintain centering thereof. Other centering techniques are disclosed in U.S. Pat. No. 3,354,973 and U.S. Pat. No. 2,652,241. All of the centering techniques require some form of spacer that provides the opposing force with some compression thereof to provide a certain amount of movement.
In view of the present methods for centering the piston in the load cell and resisting lateral forces thereon, there exists a need for a load cell having a self-centering piston that is not subject to damage upon incurring severe lateral forces and which is easily assembled.